The invention relates to a method of forming a protective layer for a roller used in an electrophotographic copying machine, in particular, for a roller which is used to prevent an offsetting.
Referring to FIG. 1, a roll or roller includes a core metal 1 having a rubber layer 2, such as formed with silicone rubber, for example, formed thereon. An injection nozzle 3 is disposed adjacent the roll, and is operated to apply a spray of rubber solution, which may be silicone rubber, fluorine-contained rubber or silicone rubber fluoride, for example, thereto while rotating the core metal 1, thus forming a protective layer 4. As will be noted from FIG. 1, the end face 5 of the protective layer 2 remains uncovered by the spray solution during such process, but the solution stays around the lower end thereof to form a bead 6, preventing a uniform diameter from being achieved.
Unless the end face 5 is sealed when the roll is used for anti-offset purposes, oil such as silicone oil, for example, may penetrate in the layer 2 between the core metal 1 and the layer 2 and between the layers 2 and 4 to cause a swelling and resulting in degradation of the layer 2. To overcome this difficulty, a sealing solution may be applied to the end face as shown in FIG. 2. However, the surface tension in the liquid applied causes the sealing surface 7 to rise or become protuberant in the middle portion and to be held low around the opposite ends, preventing a satisfactory seal from being achieved at the boundaries with the core metal 1 and the protective layer 4.